High Data Rate (HDR) is an emerging mobile wireless access technology that enables personal broadband Internet services to be accessed anywhere, anytime (see P. Bender, et al., “CDMA/HDR: A Bandwidth-Efficient High-Speed Wireless Data Service for Nomadic Users”, IEEE Communications Magazine, July 2000, and 3GPP2, “Draft Baseline Text for 1xEV-DO,” Aug. 21, 2000). Developed by Qualcomm, HDR is an air interface optimized for Internet Protocol (IP) packet data services that can deliver a shared forward link transmission rate of up to 2.46 Mbit/s per sector using only (1×) 1.25 MHz of spectrum. Compatible with CDMA2000 radio access (TIA/EIA/IS-2001, “Interoperability Specification (IOS) for CDMA2000 Network Access Interfaces,” May 2000) and wireless IP network interfaces (TIA/EIA/TSB-115, “Wireless IP Architecture Based on IETF Protocols,” Jun. 6, 2000, and TIA/EIA/IS-835, “Wireless IP Network Standard,” 3rd Generation Partnership Project 2 (3GPP2), Version 1.0, Jul. 14, 2000), HDR networks can be built entirely on IP technologies, all the way from the mobile Access Terminal (AT) to the global Internet, thus taking advantage of the scalability, redundancy and low-cost of IP networks.
An EVolution of the current 1xRTT standard for high-speed data-only (DO) services, also known as the 1xEV-DO protocol has been standardized by the Telecommunication Industry Association (TIA) as TIA/EIA/IS-856, “CDMA2000 High Rate Packet Data Air Interface Specification”, 3GPP2 C.S0024-0, Version 4.0, Oct. 25, 2002, which is incorporated herein by reference. Revision A to this specification has been published as TIA/EIA/IS-856, “CDMA2000 High Rate Packet Data Air Interface Specification”, 3GPP2 C.S0024-A, Version 2.0, June 2005. Revision A is also incorporated herein by reference.
FIG. 1 shows a 1xEV-DO radio access network 100 with radio node controllers 102 and 104 connected to radio nodes 108, 110, and 112 over a packet network 114. The packet network 114 can be implemented as an IP-based network that supports many-to-many connectivity between the radio nodes and the radio node controllers. The packet network 114 is connected to the Internet 116 via a packet data serving node 106. Other radio nodes, radio node controllers, and packet networks (not shown in FIG. 1) can be included in the radio access network 100. The packet network 114 may be several distinct networks connecting individual radio node controllers to their associated radio nodes, or it may be a single network as shown in FIG. 1, or a combination.
Typically, each radio node controller controls 25-100 radio nodes and each radio node supports 1-4 carriers each of 1.25 MHz of bandwidth. A carrier is a band of radio frequencies used to establish airlinks with access terminals. The geographic area of the radio access network that is served by any given radio node is referred to as a cell. Each cell can be divided into multiple sectors (typically 3 or 6) by using multiple sectorized antennas (the term “sector” is used both conventionally and in this document, however, even when there is only one sector per cell).
Access terminals 118 communicate with the network 100 over airlinks 120. Each access terminal may be a cellular phone, a laptop computer, a Personal Digital Assistant (PDA), a dual-mode voice/data handset, or another device, with built-in 1xEV-DO Rev-0 or Rev-A support. The airlink 120 between the network 100 and an access terminal 118 includes a control channel over which a serving radio node controller (i.e., the radio node controller on which a 1xEV-DO session of the access terminal 118) transmits messages and parameters that the access terminal 118 may need for access and paging operations. The messages and parameters (collectively referred to in this description as “control channel messages”) convey system parameters, access parameters, neighbor lists, paging messages, and channel assignment information to the access terminal 118.
FIG. 2 shows a network coverage area corresponding to the 1xEV-DO radio access network 100. In this example, the radio nodes serve coverage areas of different sizes. The large coverage areas served by radio nodes 108 and 110 are referred to as macro cells, while the smaller coverage areas served by radio node 112 is referred to as a pico cell. A macro cell covers a very large geographic area; for example, the metropolitan area of a city. A pico cell generally has a much smaller coverage area; for example, a single office building. The coverage area of a pico cell may partially or completely overlap the coverage area of a macro cell. The pico cell within the coverage area of the macro cell may operate on the same or different carrier frequency. An access terminal 118 in the pico cell coverage area may access the network either through the macro cell radio node 108 or the pico cell radio node 112. Accessing the network through the pico cell radio node 112 conserves the network resources of the macro cell and vice versa.
There are a number of different techniques that may be implemented by the 1xEV-DO radio access network 100 to determine when a handoff between the radio nodes of overlapping pico and macro cells is to take place. One example technique involves installing, in the coverage area of the macro cell radio node, a pilot beacon that transmits a pilot signal on the same carrier frequency as that of the macro cell radio node 108. A handoff can be triggered by the network upon detection of a carrier frequency change. However, these pilot beacons do not provide any actual carrier service to an access terminal and are therefore very limited in application. Additionally installation of each pilot beacon can be very expensive. Another example technique involves configuring an access terminal to constantly assume the presence of a pico cell and attempt to connect to it. However, such constant activity is very draining on the limited access terminal resources, including the access terminal's battery. Furthermore, this technique does not enable the network to determine instances in which it may be more beneficial to serve the access terminal via the macro cell radio node, although weaker pico cell signals may be available.